1. Field of the Invention
The invention relates to dc motors, and more particularly to a structure for holding terminals or brush springs thereof.
2. Related Art
Dc motors are generally driven by direct current and rectify current flowing in their rotor using a brush body (brush springs and terminals) 40 and a commutator.
An exemplary dc motor will be described with reference to the drawings. In FIG. 7, an end plate 38 is fitted to and fixed on an open end of a bottomed cylindrical motor frame 21. The end plate 38 has a recessed portion in the middle thereof, and has brush body holders 29, 29 that are fixed while passing through the end plate 38 in the thickness direction. The brush body holders 29, 29 are formed of an insulating resin or the like so as to interpose the recessed portion therebetween. In each brush body holder 29 is a plurality of terminals (a part of the brush body 40) 30 firmly embedded by pressure. The terminals serve to supply the power. Base end portions of brush springs (a part of the brush body 40) 28 are mounted on the terminals 30, each brush spring 28 extending in a direction orthogonal to a rotating shaft (described later). The front end portion of each brush spring 28 is divided into a plurality of slits. A magnet 22 is mounted on an inner circumferential surface of the motor frame 21, and a through hole is formed on the upper middle portion thereof. Bearings 33, 33' are mounted on the through hole on the upper middle portion of the motor frame 21 and the recessed portion in the middle of the end plate 38, respectively. The rotating shaft 27 is inserted into the central holes of the bearings 33, 33', so that the rotating shaft 27 is supported by the bearings 33, 33' so as to be rotatable relative to the motor frame 21 and the end plate 38. A rotor core 23 is mounted on the rotating shaft 27 substantially in the middle thereof lengthwise. The rotor core 23 is formed by laminating a plurality of core elements made of a magnetic material. The rotor core 23 has a plurality of salient poles on the outer circumference thereof. A winding 24 is wound around each of these salient poles to thereby form a rotor 25. The outer circumferential surface of the rotor core 23 confronts the magnet 22 mounted on the inner circumferential wall of the motor frame 21.
A commutator 36 is mounted at a lower portion below the rotor core 23 of the rotating shaft 27 as viewed in FIG. 7. The commutator 36 is cylindrical and has a plurality of partially cylindrical segments mounted on the surface thereof. The front end portion of each of the brush springs 28, 28 abuts against the surface of the commutator 36, and by controlling the driving of the winding 24 through the commutator 36, the rotor 25 is energized to thereby rotate the rotating shaft 27. An example of such a dc motor is disclosed in Japanese Utility Model Unexamined Publication No. 54754/1989.
As described above, the conventional dc motor is generally arranged so that the terminal 30 is fixed on the brush body holder 29 by pressure. However, such arrangement may, in some cases, allow the terminal 30 inside the motor to come out of the brush body holder 29 when the motor receives thermal stress and mechanical stress from outside. Further, vibration of the brush springs 28 is transmitted to the brush body holders 29 through the terminals 30, thereby not allowing the brush body holders 29 to absorb such vibration adequately. As a result, the vibration becomes the source of mechanical noise.